ES2727177T3 - Ferritic Stainless Steel Sheet - Google Patents

Abstract

Ferritic stainless steel sheet having a chemical composition containing, in% by mass, C: from 0.001% to 0.020%, Si: from 0.05% to 0.15%, Mn: from 0.05% to 1, 00%, P: 0.040% or less, S: 0.030% or less, Al: 0.001% to 0.15%, Cr: 20.0% to 23.0%, Ni: 0.01% at 0.80%, Cu: from 0.30% to 0.80%, Ti: from 0.10% to 0.50%, Nb: from 0.010% to 0.155%, Zr: from 0.005% to 0.155%, N: 0.020% or less, optionally one, two or more selected from Co: from 0.01% to 0.50%, Mo: from 0.01% to 0.30% and W: from 0.01% to 0.50%, optionally one, two or more selected from V: from 0.01% to 0.50%, B: from 0.0003% to 0.0030%, Mg: from 0.0005% to 0.0100 %, Ca: from 0.0003% to 0.0030%, Y: from 0.001% to 0.20% and REM rare earth metal: from 0.001% to 0.10%, optionally one or both selected from Sn: from 0.001% to 0.50% and Sb: from 0.001% to 0.50%, and the rest being Fe and unavoidable impurities, in which the expression of relation (1) is satisfied below: ** Formula ** in the that each one of Zr, Nb and Ti in relation expression (1) indicates the mass content of the corresponding chemical element.

Description

DESCRIPTION

Ferritic Stainless Steel Sheet

Technical field

The present invention relates to a ferritic stainless steel sheet that has excellent corrosion resistance, only a small amount of surface defects and excellent toughness.

Prior art

A ferritic stainless steel sheet, which does not contain Ni in a large quantity, is a material that has a lower price and more excellent price stability than those of an austenitic stainless steel sheet. In addition, ferritic stainless steel sheets are used in various applications such as construction materials, transport machines, appliances and kitchen appliances, since they have excellent resistance to rust.

The kind of ferritic stainless steel sheet that is particularly used in a strongly corrosive environment is a SUS443J1 (JIS G 4305) type stainless steel sheet, which has excellent corrosion resistance equivalent to that of a stainless steel sheet. type SUS304 (JIS G 4305, based on Cr 18% by mass-Ni 8% by mass), which is an austenitic stainless steel, as a result of containing 20.0% by mass to 23.0% by mass of Cr, from 0.3% by mass to 0.8% by mass of Cu and sufficient amounts of stabilizing chemical elements (Ti, Nb and Zr).

The commonly used SUS443J1 type stainless steel class is SUS443J1 stainless steel that mainly contains Ti as a stabilizing chemical element. Such steel is excellent in workability because texture growth is promoted as a result of containing Ti. Furthermore, since such steel is sufficiently softened even in the case where cold-annealing lamination of the sheet is carried out at a temperature lower than that of the steel containing Nb, it is possible to manufacture such steel using a cold rolling line. -recoated of the sheet and pickling that is used for common steel, which results in high productivity. However, in the case of SUS443J1 stainless steel that contains Ti, there may be a case where soybeans (surface defects) occur on the surface, which deteriorate the aesthetic appearance. It is known that the soybeans mentioned above are caused by thick TiN that forms on the surface when casting. In addition, there is the problem of low toughness with SUS443J1 stainless steel that contains Ti. This is because thick TiN is formed, which becomes a preferred starting point where fracture occurs.

Patent document 1 and patent document 2 describe the prevention of surface defects and the improvement of toughness with respect to ferritic stainless steel containing Ti.

Patent document 1 discloses a method for manufacturing ferritic stainless steel containing Ti that has excellent resistance to nerve formation and good surface quality. In patent document 1, the surface defect of an annealed and cold rolled steel sheet is avoided by controlling the solidification temperature of the steel, the casting temperature and the precipitation temperature of TiN in the steel so that it is satisfied a specified ratio in order to control the precipitation of TiN when molten steel is cast.

Patent document 2 discloses a ferritic stainless steel sheet that has excellent toughness and good corrosion resistance and is excellent in terms of productivity and economic efficiency and a method for manufacturing the steel sheet. In patent document 2, the toughness of an annealed and hot rolled steel sheet and the toughness of an annealed and cold rolled steel sheet are improved by allowing nitrides in the ZrN-shaped steel.

WO 2008/082096 A1 discloses a high chromium ferritic stainless steel with excellent corrosion resistance and excellent resistance to color alteration.

List of mentions

Patent documents

PTL 1: Japanese Unexamined Patent Application Publication No. Hei 1-118341

PTL 2: Japanese Unexamined Patent Application Publication No. 2011-214060

Summary of the invention

Technical problem

Today, in response to the diversification of household appliances, there is a demand for a ferritic stainless steel sheet that produces both a decrease in soybeans on the surface and excellent toughness as well as excellent resistance to corrosion

However, in the case of the method according to patent document 1, since TiN is precipitated on purpose in order to obtain the effect of increasing the equiaxial crystalline ratio of a roughing, it is not possible to achieve a sufficient amount of improvement of the toughness and reduction of surface defects. In the case of the method according to patent document 2 also, since it is not possible to sufficiently prevent the formation of TiN in the steel, it is not possible to obtain a sufficient effect of improving the toughness and reduction of surface defects.

An object of the present invention is to provide an excellent ferritic stainless steel sheet in corrosion resistance in which there is at the same time a decrease in the amount of surface defects and an improvement in toughness and which is sufficiently softened even in the case in which cold-annealing lamination of the sheet is carried out at a temperature equivalent to that of SUS443J1 stainless steel containing conventional Ti.

Solution to the problem

The present inventors, in response to the problems described above, conducted thorough investigations in order to produce a decrease in the amount of surface defects and an improvement in toughness at the same time and, as a result, found that it is possible to improve the toughness of SUS443J1 type stainless steel containing Ti by adding appropriate amounts of Zr and Nb in combination with SUS443J1 type stainless steel containing Ti in order to change the form of TiN precipitation, which causes a deterioration in toughness, without an increase in the cold-annealing lamination temperature of the sheet. In addition, it was found that, since it is possible to precipitate Ti-based inclusions in a finely dispersed form by this effect, it is possible to decrease the amount of surface defects of a steel sheet caused by TiN.

Specifically, it was found that, by controlling the content of the stabilizing chemical elements (Ti, Nb and Zr) in the chemical composition of a ferritic stainless steel plate of the type SUS443J1 so that the content of Ti, which is the main chemical stabilizing element , from 0.10% by mass to 0.50% by mass, the content of Nb, which is equal to or less than the content of Ti, is from 0.010% by mass to 0.150% by mass, and the content of Zr , which is equal to or less than the Nb content, from 0.005% by mass to 0.155% by mass, it is possible to allow sufficient softening to occur even when cold-annealing lamination of the sheet is carried out at a temperature equivalent to of a case in which a stabilizing chemical element is limited to Ti, and it is possible to produce a decrease in the amount of surface defects and a high tenacity at the same time. The mechanism of this is supposed to be as follows.

As a result of which Nb and Zr are contained in combination in the steel, since complex carbonitrides of Ti, Zr and Nb ((Ti, Zr, Nb) (C, N)) precipitate in dispersed form, whose particle size is smaller that of TiN formed in ferritic stainless steel containing only Ti, there is an improvement in toughness and a decrease in the amount of surface defects.

The present invention is based on the findings described above, and the subject of the present invention is as follows.

[1] A ferritic stainless steel sheet having a chemical composition containing, in mass%, C: from 0.001 to 0.020%, Si: from 0.05% to 0.15%, Mn: from 0.05% at 1.00%, P: 0.040% or less, S: 0.030% or less, Al: from 0.001% to 0.15%, Cr: from 20.0% to 23.0%, Ni: from 0 , 01% to 0.80%, Cu: from 0.30% to 0.80%, Ti: from 0.10% to 0.50%, Nb: from 0.010% to 0.150%, Zr: from 0.005% to 0.150%, N: 0.020% or less, optionally one, two or more selected from Co: from 0.01% to 0.50%, Mo: from 0.01% to 0.30% and W: from 0, 01% to 0.50%, optionally one, two or more selected from V: from 0.01% to 0.50%, B: from 0.0003% to 0.0030%, Mg: from 0.0005% to 0.0100%, Ca: from 0.0003% to 0.0030%, Y: from 0.001% to 0.20%, and REM rare earth metal: from 0.001% to 0.10%, optionally one or both selected of Sn: from 0.001% to 0.50% and Sb: from 0.001% to 0.50%, and the rest being Fe and unavoidable impurities, in which the expression of relation (1) below is satisfied;

Zr <Nb <Ti (1)

in which each of Zr, Nb and Ti in the expression of ratio (1) indicates the mass content of the corresponding chemical element.

[2] The ferritic stainless steel sheet according to item [1], the steel sheet having the chemical composition containing, in mass%, one, two or more selected Co: from 0.01% to 0.50 %, Mo: from 0.01% to 0.30% and W: from 0.01% to 0.50%.

[3] The ferritic stainless steel sheet according to item [1] or [2], the steel sheet having the chemical composition containing, in mass%, one, two or more selected from V: 0.01% at 0.50%, B: from 0.0003% to 0.0030%, Mg: from 0.0005% to 0.0100%, Ca: from 0.0003% to 0.0030%, Y: from 0.001% at 0.20% and REM (rare earth metal): from 0.001% to 0.10%.

[4] The ferritic stainless steel sheet according to any one of items [1] to [3], the steel sheet having the chemical composition containing, in mass%, one or both selected from Sn: from 0.001% to 0.50% and Sb: from 0.001% to 0.50%.

Advantageous effects of the invention

According to the present invention, it is possible to obtain a ferritic stainless steel sheet that has excellent corrosion resistance, only a small amount of surface defects and excellent toughness.

In addition, since sufficient softening occurs by performing cold-annealing lamination of the sheet at a temperature equivalent to that of a case in which a stabilizing chemical element is limited to Ti, there is an improvement in the productivity of a sheet steel ferritic stainless

Brief description of the drawings

Figure 1 is a diagram illustrating the influence of the content of Ti and Nb on the toughness and the amount of surface defects in the condition of Zr <Nb.

Figure 2 is a diagram illustrating the influence of the content of Nb and Zr on the toughness and the amount of surface defects in the condition of Nb <Ti.

Description of realizations

Hereinafter, the embodiments of the present invention will be described. Here, the present invention is not limited to the embodiments described below.

The chemical composition of the ferritic stainless steel sheet according to the present invention is defined in the claims.

Hereinafter, each of the constituent chemical elements will be described. "%" Used when describing the content of a constituent chemical element means "% by mass", unless otherwise indicated.

C: from 0.001 to 0.020%

C is a chemical element that is effective in improving the strength of steel. An effect of this type is obtained in the case where the C content is 0.001% or more. However, in the case where the C content is more than 0.020%, there is a significant deterioration in corrosion resistance and workability. Therefore, the C content is set to be 0.020% or less, preferably 0.015% or less, or more preferably 0.010% or less.

Yes: from 0.05% to 0.15%

Si is a chemical element that is effective as a deoxidizing agent. An effect of this type is obtained in the case where the Si content is 0.05% or more. However, in the case where the Si content is more than 0.40%, there is a deterioration in workability due to an increase in the hardness of the steel. In addition, in the case where the Si content is more than 0.40%, since there is a decrease in the amount of scale formed on the top surface of a roughing, which has a lubrication effect when lamination is performed In hot, there is an increase in the amount of surface defects. Therefore, the Si content is limited to be in the range of 0.05% to 0.15%. It is more preferable that the lower limit of the Si content be 0.08% or more.

Mn: from 0.05% to 1.00%

Mn has a deoxidant function. An effect of this type of Mn is obtained in the case where the content of Mn is 0.05% or more. On the other hand, in the case where the content of Mn is more than 1.00%, since precipitation and granulation of MnS are promoted, there is a deterioration in corrosion resistance. Therefore, the content of Mn is limited to be in the range of 0.05% to 1.00%. It is preferable that the lower limit of the Mn content is 0.10% or more, or more preferably 0.15% or more. It is preferable that the upper limit Mn content is less than 0.30%, or more preferably 0.25% or less.

P: 0.040% or less

P is a chemical element that deteriorates corrosion resistance. In addition, there is a deterioration in hot workability as a result of the segregation of P in the grain boundaries. Therefore, it is desirable that the P content be as small as possible, and the P content is set to be 0.040% or less, or preferably 0.030% or less.

S: 0.030% or less

S combines with Mn to form a precipitate, which is MnS. Since the contact surface between such MnS and the stainless steel base metal becomes a starting point where pitting corrosion occurs, there is a deterioration in corrosion resistance. Therefore, it is preferable that the S content is smaller, and the S content is set to be 0.030% or less, or preferably 0.020% or less.

Al: from 0.001% to 0.15%

Al is a chemical element that is effective for deoxidation. An effect of this type is obtained in the case where the content of Al is 0.001% or more. On the other hand, in the case where the content of Al is more than 0.15%, since there is a decrease in the amount of scale formed on the surface of a roughing, which has a lubrication effect when performed Hot rolling, there is an increase in the amount of surface defects. Therefore, the Al content is limited to be in the range of 0.001% to 0.15%. It is preferable that the lower limit of the Al content is 0.005% or more, or more preferably 0.01% or more. It is preferable that the upper limit of the Al content is 0.10% or less, or more preferably 0.05% or less.

Cr: from 20.0% to 23.0%

Cr is a chemical element that improves corrosion resistance by forming a passive film on the surface. It is not possible to achieve sufficient corrosion resistance in the case where the Cr content is less than 20.0%. On the other hand, in the case where the Cr content is more than 23.0%, there is a tendency for ^{the toughness to deteriorate due to a phase} a ^{and fragility at 475 ° C. Therefore, the Cr content is set to} be from 20.0% to 23.0%. It is preferable that the lower limit of Cr content is 20.5% or more. It is preferable that the upper limit of the Cr content is 22.0% or less, or more preferably 21.5% or less.

Ni: from 0.01% to 0.80%

Ni is a chemical element that makes it possible to maintain a passive state even at a lower pH by inhibiting an anodic reaction due to acid. That is, Ni improves corrosion resistance by notably inhibiting the progress of corrosion in an active dissolution state as a result of the increase in the effect of corrosion resistance in cracks. An effect of this type of Ni is obtained in the case where the Ni content is 0.01% or more. On the other hand, in the case where the Ni content is more than 0.80%, there is a deterioration in workability due to an increase in the hardness of the steel. Therefore, the Ni content is limited to 0.01% to 0.80%. It is preferable that the lower limit of the Ni content is 0.05% or more, or more preferably 0.10% or more. It is preferable that the upper limit of the Ni content is 0.40% or less, or more preferably 0.25% or less.

Cu: from 0.30% to 0.80%

Cu is a chemical element that improves corrosion resistance by reinforcing a passive film. On the other hand, in the case where the Cu content is excessively large, since g-Cu tends to precipitate, there is a deterioration in corrosion resistance. Therefore, the Cu content is set to be 0.30% to 0.80%. It is preferable that the lower limit of the Cu content is 0.35% or more, or more preferably 0.40% or more. It is preferable that the upper limit of the Cu content is 0.60% or less, or more preferably 0.45% or less.

Ti: from 0.10% to 0.50%

Ti is a chemical element that improves corrosion resistance by preventing sensitization due to Cr carbonitrides as a result of the fixation of C and N. However, TiN, which is formed as a result of containing Ti, causes deterioration in the tenacity. In the present invention, the deterioration in the toughness mentioned above due to Ti is suppressed by the combination effect of Nb and Zr as described below. The effect of improving corrosion resistance through the use of Ti is obtained in the case where the Ti content is 0.10% or more. On the other hand, in the case where the Ti content is more than 0.50%, there is a deterioration in workability due to an increase in the hardness of a stainless steel sheet. In addition, in the case where the Ti content is more than 0.50%, since it is difficult to control the form of precipitation of Ti-based inclusions even in the case where Nb and Zr are contained, there is a deterioration in surface quality. Therefore, the Ti content is set to be in the range of 0.10% to 0.50%. It is preferable that the lower limit of the Ti content is 0.15% or more, or more preferably 0.18% or more. It is preferable that the upper limit of the Ti content is 0.35% or less, or more preferably 0.26% or less.

Nb: from 0.010% to 0.150%

Nb is, like Ti, a chemical element that improves corrosion resistance by preventing sensitization due to Cr carbonitrides as a result of the fixation of C and N. In addition, Nb improves toughness and inhibits the occurrence of a defect. surface by the combination effect with Zr described below. Such effects are obtained in the case where the Nb content is 0.010% or more. On the other hand, in the case where the Nb content is more than 0,150%, there is a deterioration in workability due to an increase in the hardness of a stainless steel sheet. In addition, in the case where the Nb content is more than 0.150%, since there is an increase in the recrystallization temperature, there is a deterioration in the workability. Therefore, the content of Nb is set to be in the range of 0.010% to 0.150%. It is preferable that the lower limit of the Nb content is 0.030% or more, or more preferably 0.070% or more. It is preferable that the upper limit of the Nb content is less than 0.100%, or more preferably 0.090% or less.

Zr: from 0.005% to 0.150%

Zr is, like Ti, a chemical element that improves corrosion resistance by preventing sensitization due to Cr carbonitrides as a result of the fixation of C and N. In addition, Zr improves toughness and inhibits the occurrence of a defect. surface by the combination effect with Nb described below. It is necessary that the content of Zr be 0.005% or more in order to obtain such effects. On the other hand, in the case where the content of Zr is more than 0,150%, since inclusions based on Zr precipitate on the surface, there is an increase in the amount of surface defects. Therefore, the content of Zr is limited to be in the range of 0.005% to 0.150%. It is preferable that the lower limit of the Zr content is 0.010% or more, or more preferably 0.030% or more. It is preferable that the upper limit of the Zr content is less than 0.100%, or more preferably 0.080% or less.

It was found that, in the present invention, by containing Nb and Zr in combination with SUS443J1 stainless steel containing only Ti as a stabilizing chemical element, it is possible to allow sufficient softening to occur by performing cold-annealing lamination of the sheet even at a temperature equivalent to that of the case in which a stabilizing chemical element is limited to Ti, and it is possible to produce a decrease in the amount of surface defects and a high tenacity at the same time. Specifically, it was found that, by controlling the content of the stabilizing chemical elements (Ti, Nb and Zr) in the chemical composition of a SUS443J1 type stainless steel so that the Ti content is 0.10% to 0.50% , the content of Nb is from 0.010% to 0.150% and the content of Zr is from 0.005% to 0.150% in the condition expressed by the expression of ratio (1) below, it is possible to allow sufficient softening to occur by rolling in cold-annealing of the sheet even at a temperature equivalent to that in the case where a stabilizing chemical element is limited to Ti, and it is possible to produce a decrease in the amount of surface defects and high toughness at the same time. The mechanism of this is supposed to be as follows.

It is considered that, as a result of which Nb and Zr are contained in combination in the steel, since complex carbonitrides of Ti, Zr and Nb ((Ti, Zr, Nb) (C, N)) precipitate dispersed particle size is smaller than that of TiN formed in ferritic stainless steel containing only Ti, there is an improvement in toughness and a decrease in the amount of surface defects. In order to form the complex carbonitrides mentioned above ((Ti, Zr, Nb) (C, N)) in sufficient quantities, it is necessary that the expression of relationship (1) below be satisfied.

Zr <Nb <Ti (1)

In this case, each of Zr, Nb and Ti in the relationship expression (1) indicates the content (mass%) of the corresponding chemical element.

With respect to the relationship between Ti and Nb, it is preferable that the expression of Ti> 1.5Nb ratio, or more preferably Ti> 2Nb, be satisfied. With respect to the relationship between Nb and Zr, it is preferable that the expression of ratio Nb> 1.3Zr, or more preferably Nb> 1.5Zr, be satisfied.

N: 0.020% or less

N is a chemical element that inevitably mixes in steel. However, in the case where the N content is more than 0.020%, there is a significant deterioration in corrosion resistance and workability. Therefore, the content of N is set to be 0.020% or less, or preferably 0.015% or less.

The basic constituent chemical elements are described above, and the chemical elements described below may be appropriately added in addition to the basic constituent chemical elements in the present invention.

Co: from 0.01% to 0.50%

Co is a chemical element that improves corrosion resistance in stainless steel cracks. An effect of this type of Co is obtained in the case where the Co content is 0.01% or more. However, in the case where the Co content is more than 0.50%, an effect of this type of Co is saturated, and there is a deterioration in workability. Therefore, in the case where Co is contained, the Co content is set to be 0.01% to 0.50%. It is preferable that the lower limit of the Co content is 0.02% or more, or more preferably 0.03% or more. It is preferable that the upper limit of the Co content is 0.30% or less, or more preferably 0.10% or less.

Mo: from 0.01% to 0.30%

The Mo is effective for improving corrosion resistance in stainless steel cracks. An effect of this type is obtained in the case where the Mo content is 0.01% or more. However, in the case where the Mo content is more than 0.30%, an effect of this type of Mo is saturated, and there is a deterioration in toughness due to the formation of thick intermetallic compounds. Therefore, in the case where Mo is added, the Mo content is set to be 0.01% to 0.30%. It is preferable that the lower limit of the Mo content is 0.02% or more, or more preferably 0.03% or more. It is preferable that the upper limit of the Mo content is 0.20% or less, or more preferably 0.10% or less.

W: from 0.01% to 0.50%

W is a chemical element that improves corrosion resistance in stainless steel cracks. An effect of this type of W is obtained in the case where the content of W is 0.01% or more. On the other hand, in the case where the content of W is more than 0.50%, an effect of this type of W is saturated, and there is a deterioration in workability. Therefore, in the case where W is contained, the content of W is set to be 0.01% to 0.50%. It is preferable that the lower limit of the W content be 0.02% or more, or more preferably 0.03% or more. It is preferable that the upper limit of the W content is 0.30% or less, or more preferably 0.10% or less.

V: from 0.01% to 0.50%

V is a chemical element that improves corrosion resistance in stainless steel cracks. An effect of this type of V is obtained in the case where the content of V is 0.01% or more. On the other hand, in the case where the content of V is more than 0.50%, an effect of this type of V is saturated, and there is a deterioration in workability. Therefore, in the case where V is added, the content of V is set to be 0.01% to 0.50%, preferably 0.01% to 0.30% or more preferably 0, 01% to 0.10%.

B: from 0.0003% to 0.0030%

Since B is a chemical element that improves hot workability and secondary workability, it is effective to contain B in steel containing Ti. An effect of this type of B is obtained in the case where the content of B is 0.0003% or more. On the other hand, in the case where the content of B is more than 0.0030%, there is a deterioration in the toughness. Therefore, in the case where B is contained, the B content is set to be in the range of 0.0003% to 0.0030%. It is preferable that the lower limit of the B content be 0.0015% or more. It is preferable that the upper limit of the B content is 0.0025% or less.

Mg: 0.0005% to 0.0100%

Mg works as a deoxidizing agent together with Al forming Mg oxides in molten steel. An effect of this type of Mg is obtained in the case where the Mg content is 0.0005% or more. On the other hand, in the case where the Mg content is more than 0.0100%, there is a deterioration in the workability and a deterioration in the toughness of the steel. Therefore, in the case where Mg is contained, the Mg content is limited to be in the range of 0.0005% to 0.0100%. It is preferable that the lower limit of the Mg content is 0.0010% or more. It is preferable that the upper limit of the Mg content is 0.0050% or less, or more preferably 0.0030% or less.

Ca: from 0.0003% to 0.0030%

Ca is a chemical element that improves hot workability. An effect of this type of Ca is obtained in the case where the Ca content is 0.0003% or more. On the other hand, in the case where the Ca content is more than 0.0030%, there is a deterioration in the toughness of the steel, and there is a deterioration in corrosion resistance due to the precipitation of CaS. Therefore, in the case where Ca is added, the Ca content is limited to be in the range of 0.0003% to 0.0030%. It is preferable that the lower limit of the Ca content is 0.001% or more. It is preferable that the upper limit of the Ca content is 0.002% or less.

Y: from 0.001% to 0.20%

Y is a chemical element that improves purity by inhibiting a decrease in the viscosity of molten steel. An effect of this type of Y is obtained in the case where the content of Y is 0.001% or more. On the other hand, in the case where the content of Y is more than 0.20%, an effect of this type of Y is saturated, and there is a deterioration in workability. Therefore, in the case where Y is added, the content of Y is limited to be in the range of 0.001% to 0.20%, or preferably 0.001% to 0.10%.

REM (rare earth metal): from 0.001% to 0.10%

REM (rare earth metal: one of the chemical elements that have atomic numbers from 57 to 71 such as La, Ce or Nd) is a chemical element that improves resistance to high temperature oxidation. An effect of this type of REM is obtained in the case where the content of REM is 0.001% or more. On the other hand, in the case where the REM content is more than 0.10%, an effect of this type of REM is saturated, and a surface defect occurs when hot rolling. Therefore, in the case where REM is contained, the REM content is limited to be in the range of 0.001% to 0.10%. It is preferable that the lower limit of the REM content be 0.005% or more. It is preferable that the upper limit of the REM content be 0.05% or less.

Sn: from 0.001% to 0.50%

The Sn is effective in improving the resistance to the formation of valleys by promoting the formation of a deformation zone when lamination is performed. An effect of this type is obtained in the case where the content of Sn is 0.001% or more. However, in the case where the content of Sn is more than 0.50%, an effect of this type of Sn is saturated, and there is a deterioration in workability. Therefore, in the case where Sn is added, the content of Sn is set to be from 0.001% to 0.50%. It is preferable that the lower limit of the Sn content is 0.003% or more. It is preferable that the upper limit of the Sn content is 0.20% or less.

Sb: from 0.001% to 0.50%

The Sb is effective in improving the resistance to the formation of valleys by promoting the formation of a deformation zone when rolling. An effect of this type is obtained in the case where the content of Sb is 0.001% or more. However, in the case where the content of Sb is more than 0.50%, an effect of this type of Sb is saturated, and there is a deterioration in workability. Therefore, in the case where Sb is contained, the content of Sb is set to be from 0.001% to 0.50%. It is preferable that the lower limit of the Sb content is 0.003% or more. It is preferable that the upper limit of the Sb content is 0.20% or less.

The rest, which is different from the constituent chemical elements described above, is Fe and inevitable impurities. Representative examples of the inevitable impurities described herein include H, O (oxygen), Zn, Ga, Ge, As, Ag, En, Hf, Ta, Re, Os, Ir, Pt, Au and Pb. Among these chemical elements, H and O (oxygen) may be contained in an amount of 0.05% or less. Other chemical elements may be contained in an amount of 0.3% or less.

Hereinafter, a preferable method for manufacturing the ferritic stainless steel sheet according to the present invention will be described. Molten steel is prepared having the chemical composition described above using a known method such as one that uses a converter, an electric furnace or a vacuum melting furnace and is converted into a steel material (roughing) using a continuous casting method. or a method of ingot-grinding casting. This steel material is heated to a temperature of 1000 ° C to 1200 ° C and then subjected to hot rolling to have a thickness of 2.0 mm to 5.0 mm under the condition of a finishing temperature of 700 ° C at 1000 ° C. The hot rolled steel sheet, which has been obtained as described above, is annealed at a temperature of 800 ° C to 1100 ° C followed by pickling, cold rolling and cold-annealing lamination of the sheet a a temperature of 700 ° C to 1000 ° C. After the cold-annealing lamination of the sheet, the stripping is carried out in order to remove the scale. The cold rolled steel sheet from which the scale has been removed can undergo finishing lamination. Furthermore, the present invention is effective not only for the cold rolled sheet product mentioned above, but also for a hot rolled sheet product.

Examples

After ferritic stainless steels having the chemical compositions given in table 1 (table 1-1 and table 1-2 are combined to form table 1), table 2 (table 2-1 and table 2) -2 combine to form table 2) and table 3 (table 3-1 and table 3-2 combine to form table 3) in steel ingots having a weight of 100 kg, the ingots were heated to a temperature of 1200 ° C and subjected to hot rolling in order to obtain hot rolled steel sheets having a thickness of 4.0 mm. Subsequently, the hot-rolled steel sheets were subjected to annealing at a temperature of 1100 ° C followed by pickling that used a commonly used method and was subjected to cold rolling to have a thickness of 2.0 mm followed by annealing at a 900 ° C temperature and pickling that used a commonly used method.

By determining the pitting potential (JIS G 0577) of the cold rolled and annealed steel sheet obtained, the corrosion resistance was evaluated. A case in which the bite potential was 290 mV (versus SCE) or more was considered as “O” (satisfactory), and a case in which the bite potential was less than 290 mV (versus SCE) It was considered as “▲” (unsatisfactory).

In addition, by performing a Charpy impact test on a specimen (JIS B 7722 standard, V-groove) that had been taken from the cold rolled and annealed steel sheet obtained along the rolling direction, the toughness of The steel plate. A case in which Charpy impact value at 25 ° C was 200 J / cm2 or more was considered as "O" (satisfactory), and one case in which the Charpy impact value at 25 ° C was less than 200 J / cm2 was considered as "▲" (unsatisfactory).

In addition, observing the surface of the cold rolled and annealed steel sheet in order to determine the density of soybeans on the surface, the amount of surface defects was evaluated. Preparing 10 steel sheets that had each of the chemical compositions, and counting the number of soybeans that had a length in the L direction of more than 10 mm in a region that was 200 mm wide and 200 mm long in the central portion of the upper surface of each of the steel sheets, a case in which the average number counted was 1 or less was considered as "O" (satisfactory), and a case in which the average of the numbers counted was more than 1 was considered as "▲" (unsatisfactory).

In addition, it was evaluated whether there was sufficient softening by annealing even at a temperature of 880 ° C for 20 seconds on the cold rolled steel sheet that had not yet been annealed. The evaluation was performed comparing the hardness (a) of a steel sheet in the cold rolled state or as cold rolled, the hardness (b) of a steel sheet that had been annealed at a temperature of 880 ° C for 20 seconds and the hardness (c) of a steel sheet that had been annealed at a temperature of 1000 ° C for 20 seconds as an index of a case in which sufficient softening occurred. Three specimens having a length of 15 mm and a width of 20 mm were taken from the cold rolled steel sheet, and each of the specimens to determine respectively b and c was subjected to the corresponding annealing. Subsequently, each of the three specimens was cut into pieces that were 15 mm long and 10 mm wide. Then, the Vickers hardness determined in the cross section of the cut piece was used for evaluation. As the annealing progressed, the hardness of the steel plate changed from a to c. A case in which 90% or more of such a softening process was completed through annealing at a temperature of 880 ° C for 20 seconds, that is, a case in which the expression of relation c was satisfied 0.1 3 (ac)> b, was considered as “s” (satisfactory), and other cases were considered as “m” (unsatisfactory).

The results obtained are given in Tables 1, 2 and 3. In the case of the steels of the examples of the present invention, all the results of consideration of the pitting potential, the Charpy impact value, the surface defect and the Certain softening temperatures were "O", which means that these steels had good resistance to corrosion and toughness, only a small amount of surface defects and no manufacturing problems.

Comparative example No. 34, whose Cr content was less than the range according to the present invention, had poor corrosion resistance.

Comparative example No. 35, whose Cr content was greater than the range according to the present invention, had low toughness.

Comparative example No. 36, whose Ni content was less than the range according to the present invention, had poor corrosion resistance.

Comparative example No. 37, whose Ti content was smaller than the range according to the present invention, had poor corrosion resistance.

Comparative example No. 38, whose Ti content was greater than the range according to the present invention, had low toughness and a large number of surface defects.

Comparative example No. 39, whose Nb content was smaller than the range according to the present invention, had low toughness and a large number of surface defects.

Comparative example No. 40, whose Nb content was greater than the range according to the present invention, had poor workability due to a high softening temperature.

Comparative example No. 41, whose Zr content was smaller than the range according to the present invention, had low toughness and a large number of surface defects.

Comparative example No. 42, whose Zr content was greater than the range according to the present invention, had a large number of surface defects.

Comparative example No. 57, whose content of Nb and Zr were both smaller than the range according to the present invention, had low toughness and a large number of surface defects.

Comparative example No. 58, whose content of Ti and Zr were both smaller than the intervals according to the present invention, and whose content of Al and Nb were both greater than the intervals according to the present invention, had low toughness, a large amount of surface defects and poor workability due to a high softening temperature.

In this document, comparative examples Nos. 43 to 54, 67 and 68 will be described hereinafter with reference to Figure 1 and Figure 2.

[Table 1-2]

* [Corrosion resistance] A case in which the pitting potential was 290 mV (versus SCE) or more was considered as “O” (satisfactory), and a case in which the pitting potential was less than 290 mV (compared to SCE) was considered as “A” (unsatisfactory).

* [Charpy impact value] A case in which the Charpy impact value (of a steel sheet having a thickness of 2 mm) at 25 ° C was 200 J / cm2 or more was considered as "O" ( satisfactory), and a case in which the impact value Charpy (of a sheet of Steel having a thickness of 2 mm) at 25 ° C was less than 200 J / cm2 was considered as "A" (unsatisfactory).

* [Surface defect] A case in which the number of soybeans in a region of 200 mmW x 200 mmL was 1 or less was considered as “O” (satisfactory), and a case in which the number described above was of more than 1 it was considered as "A" (unsatisfactory).

* [Softening temperature] A case in which the expression of relation c 0.1 3 (ac)> b was satisfied was considered as “O” (satisfactory), and other cases were considered as “A” (unsatisfactory), where the Vickers hardness of a steel sheet in the cold rolled state was defined as a, the Vickers hardness of a steel sheet that had undergone a heat treatment at a temperature of 880 ° C for 20 seconds was defined as by Vickers hardness of a steel sheet that had undergone a heat treatment at a temperature of 1000 ° C for 20 seconds was defined as c.

[Table 2-2]

* [Corrosion resistance] A case in which the pitting potential was 290 mV (versus SCE) or more was considered as “O” (satisfactory), and a case in which the pitting potential was less than 290 mV (compared to SCE) was considered as “A” (unsatisfactory).

* [Charpy impact value] A case in which the Charpy impact value (of a steel sheet having a thickness of 2 mm) at 25 ° C was 200 J / cm2 or more was considered as "O" ( satisfactory), and a case in which the Charpy impact value (of a steel sheet having a thickness of 2 mm) at 25 ° C was less than 200 J / cm2 was considered as "A" (unsatisfactory).

* [Surface defect] A case in which the number of soybeans in a region of 200 mmW x 200 mmL was 1 or less was considered as “O” (satisfactory), and a case in which the number described above was of more than 1 it was considered as "A" (unsatisfactory).

* [Softening temperature] A case in which the expression of relation c 0.1 3 (ac)> b was satisfied was considered as “O” (satisfactory), and other cases were considered as “A” (unsatisfactory), where the Vickers hardness of a steel sheet in the cold rolled state was defined as a, the Vickers hardness of a steel sheet that had undergone a heat treatment at a temperature of 880 ° C for 20 seconds was defined as by Vickers hardness of a steel sheet that had undergone a heat treatment at a temperature of 1000 ° C for 20 seconds was defined as c.

[Table 3-2]

* [Corrosion resistance] A case in which the pitting potential was 290 mV (versus SCE) or more was considered as “O” (satisfactory), and a case in which the pitting potential was less than 290 mV (compared to SCE) was considered as “A” (unsatisfactory).

* [Charpy impact value] A case in which the Charpy impact value (of a steel sheet having a thickness of 2 mm) at 25 ° C was 200 J / cm2 or more was considered as "O" ( satisfactory), and a case in which the Charpy impact value (of a steel sheet having a thickness of 2 mm) at 25 ° C was less than 200 J / cm2 was considered as "A" (unsatisfactory).

* [Surface defect] A case in which the number of soybeans in a region of 200 mmW x 200 mmL was 1 or less was considered as “O” (satisfactory), and a case in which the number described above was of more than 1 it was considered as "A" (unsatisfactory).

* [Softening temperature] A case in which the expression of relation c 0.1 3 (ac)> b was satisfied was considered as “O” (satisfactory), and other cases were considered as “A” (unsatisfactory), where the Vickers hardness of a steel sheet in the cold rolled state was defined as a, the Vickers hardness of a steel sheet that had undergone a heat treatment at a temperature of 880 ° C for 20 seconds was defined as by Vickers hardness of a steel sheet that had undergone a heat treatment at a temperature of 1000 ° C for 20 seconds was defined as c.

Figure 1 illustrates the results of evaluation of Charpy impact values and surface defects of the examples of the present invention and comparative examples (Nos. 43 to 48), whose chemical compositions were within the range according to the present invention, and in those that the relationship expression Nb> Zr was satisfied and the relationship expression Ti> Nb was not satisfied, in a graph form in which the horizontal axis indicates the content of Ti and the vertical axis indicates the content of Nb. In this document, for all the steel sheets illustrated in Figure 1, in a case where the evaluation result with respect to the Charpy impact value was satisfactory, the evaluation with respect to a surface defect was satisfactory, and In a case where the evaluation result with respect to the Charpy impact value was unsatisfactory, the evaluation with respect to a surface defect was unsatisfactory. As indicated in Figure 1, it is necessary that the expression of ratio Ti> Nb be satisfied in order to produce excellent toughness and a decrease in the amount of surface defects at the same time within the range of the chemical composition according to the present invention.

Figure 2 illustrates the results of evaluation of Charpy impact values and surface defects of the examples of the present invention and comparative examples (Nos. 49 to 54, 67 and 68), whose chemical compositions were within the range according to the present invention, and in which the expression of relation Ti> Nb was satisfied and the expression of relation Nb> Zr was not satisfied, in a graph form in which the horizontal axis indicates the content of Nb and the vertical axis indicates the content of Zr. As indicated in Figure 2, it is necessary that the expression of relation Nb> Zr be satisfied in order to produce excellent toughness and a decrease in the amount of surface defects at the same time within the range of the chemical composition according to the present invention. In addition, as indicated in Figure 1 and Figure 2, it is clarified that it is necessary that both the Ti> Nb relationship expression and the Nb> Zr relationship expression be satisfied, that is, the Zr <Nb <Ti relationship expression , in order to produce excellent toughness and a decrease in the amount of surface defects at the same time inside of the range of the chemical composition according to the present invention.

Herein, comparative examples Nos. 55 and 56, whose chemical compositions were within the range according to the present invention, and in which the expression of Ti> Nb ratio or the expression of Nb> Zr ratio was not satisfied, they were unsatisfactory in evaluations both with respect to the Charpy impact value and with respect to the surface defect.

Industrial applicability

The ferritic stainless steel sheet according to the present invention, which has excellent toughness and only a small amount of surface defects, can preferably be used not only for parts that are required to have satisfactory corrosion resistance but also for parts to be requires that they have satisfactory toughness and surface quality including interior elevator panels, interiors, hoods, mufflers, cabinets, home appliance parts, office appliance parts, car interior parts, car exhaust pipes, construction materials , drainage channel covers, sea containers, household goods, kitchen appliances, interior and exterior building materials, auto parts, escalators, rail vehicles, the chassis of electrical appliances and the like.

Claims (1)

^{Ferritic stainless steel sheet having a chemical composition containing, in mass} % ^{, C: from} 0.001% to 0.020%, Si: from 0.05% to 0.15%, Mn: from 0.05% to 1, 00%, P: 0.040% or less, S: 0.030% or less, Al: 0.001% to 0.15%, Cr: 20.0% to 23.0%, Ni: 0.01% at 0.80%, Cu: from 0.30% to 0.80%, Ti: from 0.10% to 0.50%, Nb: from 0.010% to 0.155%, Zr: from 0.005% to 0.155%, N: 0.020% or less, optionally one, two or more selected from Co: from 0.01% to 0.50%, Mo: from 0.01% to 0.30% and W: from 0.01% to 0.50%, optionally one, two or more selected from V: from 0.01% to 0.50%, B: from 0.0003% to 0.0030%, Mg: from 0.0005% to 0.0100 %, Ca: from 0.0003% to 0.0030%, Y: from 0.001% to 0.20% and REM rare earth metal: from 0.001% to 0.10%, optionally one or both selected from Sn: from 0.001% to 0.50% and Sb: from 0.001% to 0.50%, and the rest being Fe and inevitable impurities, in which the expression of relation (1) is satisfied below: Zr <Nb <Ti (1) in which each of Zr, Nb and Ti in expression of ratio (1) indicates the mass content of the corresponding chemical element. Ferritic stainless steel sheet according to claim 1, the steel sheet having the chemical composition containing, in mass%, one, two or more selected from Co: from 0.01% to 0.50%, Mo: from 0 , 01% to 0.30% and W: from 0.01% to 0.50%. Ferritic stainless steel sheet according to claim 1 or 2, the steel sheet having the chemical composition containing, in mass%, one, two or more selected from V: from 0.01% to 0.50%, B: from 0.0003% to 0.0030%, Mg: from 0.0005% to 0.0100%, Ca: from 0.0003% to 0.0030%, Y: from 0.001% to 0.20% and metal Rare earth REM: from 0.001% to 0.10%. Ferritic stainless steel sheet according to any one of claims 1 to 3, the steel sheet having the chemical composition containing, in mass%, one or both selected from Sn: from 0.001% to 0.50% and Sb: from 0.001% to 0.50%.